Endowing human adenovirus serotype 5 vectors with fiber domains of species B greatly enhances gene transfer into human mesenchymal stem cells

Conventional and Tropism-Modified High-Capacity Adenoviral Vectors Exhibit Similar Transduction Profiles in Human iPSC-Derived Retinal Organoids

Viral vector delivery of gene therapy represents a promising approach for the treatment of numerous retinal diseases. Adeno-associated viral vectors (AAV) constitute the primary gene delivery platform; however, their limited cargo capacity restricts the delivery of several clinically relevant retinal genes. In this study, we explore the feasibility of employing high-capacity adenoviral vectors (HC-AdVs) as alternative delivery vehicles, which, with a capacity of up to 36 kb, can potentially accommodate all known retinal gene coding sequences. We utilized HC-AdVs based on the classical adenoviral type 5 (AdV5) and on a fiber-modified AdV5.F50 version, both engineered to deliver a 29.6 kb vector genome encoding a fluorescent reporter construct. The tropism of these HC-AdVs was evaluated in an induced pluripotent stem cell (iPSC)-derived human retinal organoid model. Both vector types demonstrated robust transduction efficiency, with sustained transgene expression observed for up to 110 days post-transduction. Moreover, we found efficient transduction of photoreceptors and Müller glial cells, without evidence of reactive gliosis or loss of photoreceptor cell nuclei. However, an increase in the thickness of the photoreceptor outer nuclear layer was observed at 110 days post-transduction, suggesting potential unfavorable effects on Müller glial or photoreceptor cells associated with HC-AdV transduction and/or long-term reporter overexpression. These findings suggest that while HC-AdVs show promise for large retinal gene delivery, further investigations are required to assess their long-term safety and efficacy.

Selection-free precise gene repair using high-capacity adenovector delivery of advanced prime editing systems rescues dystrophin synthesis in DMD muscle cells

Prime editors have high potential for disease modelling and regenerative medicine efforts including those directed at the muscle-wasting disorder Duchenne muscular dystrophy (DMD). However, the large size and multicomponent nature of prime editing systems pose substantial production and delivery issues. Here, we report that packaging optimized full-length prime editing constructs in adenovector particles (AdVPs) permits installing precise DMD edits in human myogenic cells, namely, myoblasts and mesenchymal stem cells (up to 80% and 64%, respectively). AdVP transductions identified optimized prime-editing reagents capable of correcting DMD reading frames of ∼14% of patient genotypes and restoring dystrophin synthesis and dystrophin-β-dystroglycan linkages in unselected DMD muscle cell populations. AdVPs were equally suitable for correcting DMD iPSC-derived cardiomyocytes and delivering dual prime editors tailored for DMD repair through targeted exon 51 deletion. Moreover, by exploiting the cell cycle-independent AdVP transduction process, we report that 2- and 3-component prime-editing modalities are both most active in cycling than in post-mitotic cells. Finally, we establish that combining AdVP transduction with seamless prime editing allows for stacking chromosomal edits through successive delivery rounds. In conclusion, AdVPs permit versatile investigation of advanced prime editing systems independently of their size and component numbers, which should facilitate their screening and application.

Recombinant Adenoviruses for Delivery of Therapeutics Following Spinal Cord Injury

The regeneration of nerve tissue after spinal cord injury is a complex and poorly understood process. Medication and surgery are not very effective treatments for patients with spinal cord injuries. Gene therapy is a popular approach for the treatment of such patients. The delivery of therapeutic genes is carried out in a variety of ways, such as direct injection of therapeutic vectors at the site of injury, retrograde delivery of vectors, and ex vivo therapy using various cells. Recombinant adenoviruses are often used as vectors for gene transfer. This review discusses the advantages, limitations and prospects of adenovectors in spinal cord injury therapy.

Broadening the reach and investigating the potential of prime editors through fully viral gene-deleted adenoviral vector delivery

Prime editing is a recent precision genome editing modality whose versatility offers the prospect for a wide range of applications, including the development of targeted genetic therapies. Yet, an outstanding bottleneck for its optimization and use concerns the difficulty in delivering large prime editing complexes into cells. Here, we demonstrate that packaging prime editing constructs in adenoviral capsids overcomes this constrain resulting in robust genome editing in both transformed and non-transformed human cells with up to 90% efficiencies. Using this cell cycle-independent delivery platform, we found a direct correlation between prime editing activity and cellular replication and disclose that the proportions between accurate prime editing events and unwanted byproducts can be influenced by the target-cell context. Hence, adenovector particles permit the efficacious delivery and testing of prime editing reagents in human cells independently of their transformation and replication statuses. The herein integrated gene delivery and gene editing technologies are expected to aid investigating the potential and limitations of prime editing in numerous experimental settings and, eventually, in ex vivo or in vivo therapeutic contexts.

Systemic administration of mesenchymal stem cells loaded with a novel oncolytic adenovirus carrying IL-24/endostatin enhances glioma therapy

Oncolytic adenovirus-mediated gene therapy shows promise for cancer treatment; however, the systemic delivery of oncolytic adenovirus to tumors remains challenging. Recently, mesenchymal stem cells (MSCs) have emerged as potential vehicles for improving delivery. Yet, because the oncolytic adenovirus replicates in MSCs, balancing MSC viability with viral load is key to achieving optimal therapeutic effect. We thus developed an all-in-one Tet-on system that can regulate replication of oncolytic adenovirus. Then, we loaded the novel oncolytic adenovirus carrying interleukin (IL)-24 and/or Endostatin in human umbilical cord blood-mesenchymal stem cells (hUCB-MSCs) for glioma therapy. In vitro assays demonstrated that this novel oncolytic adenovirus could efficiently replicate and kill glioma cells while sparing normal cells. Moreover, doxycycline effectively regulated oncolytic adenovirus replication in the hUCB-MSCs. The doxycycline induction group with dual expression of IL-24 and Endostatin exhibited significantly greater antitumor effects than other groups in a xenograft model of glioma. Thus, this strategy for systemic delivery of oncolytic adenovirus with its oncolytic activity controlled by a Tet-on system is a promising method for achieving antitumor efficacy in glioma, especially for metastatic tumors.

Mesenchymal Stem Cells for Neurological Disorders

Neurological disorders are becoming a growing burden as society ages, and there is a compelling need to address this spiraling problem. Stem cell-based regenerative medicine is becoming an increasingly attractive approach to designing therapies for such disorders. The unique characteristics of mesenchymal stem cells (MSCs) make them among the most sought after cell sources. Researchers have extensively studied the modulatory properties of MSCs and their engineering, labeling, and delivery methods to the brain. The first part of this review provides an overview of studies on the application of MSCs to various neurological diseases, including stroke, traumatic brain injury, spinal cord injury, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease, Parkinson's disease, and other less frequently studied clinical entities. In the second part, stem cell delivery to the brain is focused. This fundamental but still understudied problem needs to be overcome to apply stem cells to brain diseases successfully. Here the value of cell engineering is also emphasized to facilitate MSC diapedesis, migration, and homing to brain areas affected by the disease to implement precision medicine paradigms into stem cell-based therapies.

Delivery systems for enhancing oncolytic adenoviruses efficacy

Oncolytic adenovirus (OAds) has long been considered a promising biotherapeutic agent against various types of cancer owing to selectively replicate in and lyse cancer cells, while remaining dormant in healthy cells. In the last years, multiple (pre)clinical studies using genetic engineering technologies enhanced OAds anti-tumor effects in a broad range of cancers. However, poor targeting delivery, tropism toward healthy tissues, low-level expression of Ad receptors on tumor cells, and pre-existing neutralizing antibodies are major hurdles for systemic administration of OAds. Different vehicles have been developed for addressing these obstacles, such as stem cells, nanoparticles (NPs) and shielding polymers, extracellular vesicles (EVs), hydrogels, and microparticles (MPs). These carriers can enhance the therapeutic efficacy of OVs through enhancing transfection, circulatory longevity, cellular interactions, specific targeting, and immune responses against cancer. In this paper, we reviewed adenovirus structure and biology, different types of OAds, and the efficacy of different carriers in systemic administration of OAds.

Adenoviral Vectors Meet Gene Editing: A Rising Partnership for the Genomic Engineering of Human Stem Cells and Their Progeny

Gene editing permits changing specific DNA sequences within the vast genomes of human cells. Stem cells are particularly attractive targets for gene editing interventions as their self-renewal and differentiation capabilities consent studying cellular differentiation processes, screening small-molecule drugs, modeling human disorders, and testing regenerative medicines. To integrate gene editing and stem cell technologies, there is a critical need for achieving efficient delivery of the necessary molecular tools in the form of programmable DNA-targeting enzymes and/or exogenous nucleic acid templates. Moreover, the impact that the delivery agents themselves have on the performance and precision of gene editing procedures is yet another critical parameter to consider. Viral vectors consisting of recombinant replication-defective viruses are under intense investigation for bringing about efficient gene-editing tool delivery and precise gene-editing in human cells. In this review, we focus on the growing role that adenoviral vectors are playing in the targeted genetic manipulation of human stem cells, progenitor cells, and their differentiated progenies in the context of in vitro and ex vivo protocols. As preamble, we provide an overview on the main gene editing principles and adenoviral vector platforms and end by discussing the possibilities ahead resulting from leveraging adenoviral vector, gene editing, and stem cell technologies.

High-Capacity Adenoviral Vectors Permit Robust and Versatile Testing of DMD Gene Repair Tools and Strategies in Human Cells

Duchenne muscular dystrophy (DMD) is a fatal X-linked muscle wasting disorder arising from mutations in the ~2.4 Mb dystrophin-encoding DMD gene. RNA-guided CRISPR-Cas9 nucleases (RGNs) are opening new DMD therapeutic routes whose bottlenecks include delivering sizable RGN complexes for assessing their effects on human genomes and testing ex vivo and in vivo DMD-correcting strategies. Here, high-capacity adenoviral vectors (HC-AdVs) encoding single or dual high-specificity RGNs with optimized components were investigated for permanently repairing defective DMD alleles either through exon 51-targeted indel formation or major mutational hotspot excision (>500 kb), respectively. Firstly, we establish that, at high doses, third-generation HC-AdVs lacking all viral genes are significantly less cytotoxic than second-generation adenoviral vectors deleted in E1 and E2A. Secondly, we demonstrate that genetically retargeted HC-AdVs can correct up to 42% ± 13% of defective DMD alleles in muscle cell populations through targeted removal of the major mutational hotspot, in which over 60% of frame-shifting large deletions locate. Both DMD gene repair strategies tested readily led to the detection of Becker-like dystrophins in unselected muscle cell populations, leading to the restoration of β-dystroglycan at the plasmalemma of differentiated muscle cells. Hence, HC-AdVs permit the effective assessment of DMD gene-editing tools and strategies in dystrophin-defective human cells while broadening the gamut of DMD-correcting agents.

Use of stem cells as carriers of oncolytic viruses for cancer treatment

Therapeutic application of stem cells and oncolytic viruses in cancer treatment has rapidly increased in the last decade. Oncolytic viruses are considered as a new class of anticancer agents because of their ability to selectively infect and destroy cancer cells. Furthermore, regarding the specific migratory capacity of stem cells, they can be used as carriers or vectors targeting metastatic cancer. Promising results have been reported regarding the use of stem cells and oncolytic viruses as a therapeutic approach for the treatment of metastatic cancer. The present review aimed to determine the approaches involved in the use of the tumor-homing capacity of stem cells for cancer treatment.

Mesenchymal Stem Cell-Mediated Delivery of an Oncolytic Adenovirus Enhances Antitumor Efficacy in Hepatocellular Carcinoma

Oncolytic virotherapy is a promising alternative to conventional treatment, yet systemic delivery of these viruses to tumors remains a major challenge. In this regard, mesenchymal stem cells (MSC) with well-established tumor-homing property could serve as a promising systemic delivery tool. We showed that MSCs could be effectively infected by hepatocellular carcinoma (HCC)-targeted oncolytic adenovirus (HCC-oAd) through modification of the virus' fiber domain and that the virus replicated efficiently in the cell carrier. HCC-targeting oAd loaded in MSCs (HCC-oAd/MSC) effectively lysed HCC cells in vitro under both normoxic and hypoxic conditions as a result of the hypoxia responsiveness of HCC-oAd. Importantly, systemically administered HCC-oAd/MSC, which were initially infected with a low viral dose, homed to HCC tumors and resulted in a high level of virion accumulation in the tumors, ultimately leading to potent tumor growth inhibition. Furthermore, viral dose reduction and tumor localization of HCC-oAd/MSC prevented the induction of hepatotoxicity by attenuating HCC-oAd hepatic accumulation. Taken together, these results demonstrate that MSC-mediated systemic delivery of oAd is a promising strategy for achieving synergistic antitumor efficacy with improved safety profiles. SIGNIFICANCE: Mesenchymal stem cells enable delivery of an oncolytic adenovirus specifically to the tumor without posing any risk associated with systemic administration of naked virions to the host.

Coating with spermine-pullulan polymer enhances adenoviral transduction of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are adult stem cells with multilineage potential, which makes them attractive tools for regenerative medicine applications. Efficient gene transfer into MSCs is essential not only for basic research in developmental biology but also for therapeutic applications involving gene-modification in regenerative medicine. Adenovirus vectors (Advs) can efficiently and transiently introduce an exogenous gene into many cell types via their primary receptors, the coxsackievirus and adenovirus receptors, but not into MSCs, which are deficient in coxsackievirus and adenovirus receptors expression. To overcome this problem, we developed an Adv coated with a spermine-pullulan (SP) cationic polymer and investigated its physicochemical properties and internalization mechanisms. We demonstrated that the SP coating could enhance adenoviral transduction of MSCs without detectable cytotoxicity or effects on differentiation. Our results argue in favor of the potentiality of the SP-coated Adv as a prototype vector for efficient and safe transduction of MSCs.

Adenoviral vectors encoding CRISPR/Cas9 multiplexes rescue dystrophin synthesis in unselected populations of DMD muscle cells

Mutations disrupting the reading frame of the ~2.4 Mb dystrophin-encoding DMD gene cause a fatal X-linked muscle-wasting disorder called Duchenne muscular dystrophy (DMD). Genome editing based on paired RNA-guided nucleases (RGNs) from CRISPR/Cas9 systems has been proposed for permanently repairing faulty DMD loci. However, such multiplexing strategies require the development and testing of delivery systems capable of introducing the various gene editing tools into target cells. Here, we investigated the suitability of adenoviral vectors (AdVs) for multiplexed DMD editing by packaging in single vector particles expression units encoding the Streptococcus pyogenes Cas9 nuclease and sequence-specific gRNA pairs. These RGN components were customized to trigger short- and long-range intragenic DMD excisions encompassing reading frame-disrupting exons in patient-derived muscle progenitor cells. By allowing synchronous and stoichiometric expression of the various RGN components, we demonstrate that dual RGN-encoding AdVs can correct over 10% of target DMD alleles, readily leading to the detection of Becker-like dystrophin proteins in unselected muscle cell populations. Moreover, we report that AdV-based gene editing can be tailored for removing mutations located within the over 500-kb major DMD mutational hotspot. Hence, this single DMD editing strategy can in principle tackle a broad spectrum of mutations present in more than 60% of patients with DMD.

Engineered Viruses as Genome Editing Devices

Genome editing based on sequence-specific designer nucleases, also known as programmable nucleases, seeks to modify in a targeted and precise manner the genetic information content of living cells. Delivering into cells designer nucleases alone or together with donor DNA templates, which serve as surrogate homologous recombination (HR) substrates, can result in gene knockouts or gene knock-ins, respectively. As engineered replication-defective viruses, viral vectors are having an increasingly important role as delivery vehicles for donor DNA templates and designer nucleases, namely, zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered, regularly interspaced, short palindromic repeats (CRISPR)-associated Cas9 (CRISPR−Cas9) nucleases, also known as RNA-guided nucleases (RGNs). We review this dual role played by engineered viral particles on genome editing while focusing on their main scaffolds, consisting of lentiviruses, adeno-associated viruses, and adenoviruses. In addition, the coverage of the growing body of research on the repurposing of viral vectors as delivery systems for genome editing tools is complemented with information regarding their main characteristics, pros, and cons. Finally, this information is framed by a concise description of the chief principles, tools, and applications of the genome editing field as a whole.

Barriers in contribution of human mesenchymal stem cells to murine muscle regeneration

AIM: To study regeneration of damaged human and murine muscle implants and the contribution of added xenogeneic mesenchymal stem cells (MSCs).

METHODS: Minced human or mouse skeletal muscle tissues were implanted together with human or mouse MSCs subcutaneously on the back of non-obese diabetic/severe combined immunodeficient mice. The muscle tissues (both human and murine) were minced with scalpels into small pieces (< 1 mm³) and aliquoted in portions of 200 mm³. These portions were either cryopreserved in 10% dimethylsulfoxide or freshly implanted. Syngeneic or xenogeneic MSCs were added to the minced muscles directly before implantation. Implants were collected at 7, 14, 30 or 45 d after transplantation and processed for (immuno)histological analysis. The progression of muscle regeneration was assessed using a standard histological staining (hematoxylin-phloxin-saffron). Antibodies recognizing Pax7 and von Willebrand factor were used to detect the presence of satellite cells and blood vessels, respectively. To enable detection of the bone marrow-derived MSCs or their derivatives we used MSCs previously transduced with lentiviral vectors expressing a cytoplasmic LacZ gene. X-gal staining of the fixed tissues was used to detect β-galactosidase-positive cells and myofibers.

RESULTS: Myoregeneration in implants of fresh murine muscle was evident as early as day 7, and progressed with time to occupy 50% to 70% of the implants. Regeneration of fresh human muscle was slower. These observations of fresh muscle implants were in contrast to the regeneration of cryopreserved murine muscle that proceeded similarly to that of fresh tissue except for day 45 (P < 0.05). Cryopreserved human muscle showed minimal regeneration, suggesting that the freezing procedure was detrimental to human satellite cells. In fresh and cryopreserved mouse muscle supplemented with LacZ-tagged mouse MSCs, β-galactosidase-positive myofibers were identified early after grafting at the well-vascularized periphery of the implants. The contribution of human MSCs to murine myofiber formation was, however, restricted to the cryopreserved mouse muscle implants. This suggests that fresh murine muscle tissue provides a suboptimal environment for maintenance of human MSCs. A detailed analysis of the histological sections of the various muscle implants revealed the presence of cellular structures with a deviating morphology. Additional stainings with alizarin red and alcian blue showed myofiber calcification in 50 of 66 human muscle implants, and encapsulated cartilage in 10 of 81 of murine muscle implants, respectively.

CONCLUSION: In mouse models the engagement of human MSCs in myoregeneration might be underestimated. Furthermore, our model permits the dissection of species-specific factors in the microenvironment.

Glioblastoma-derived extracellular vesicles modify the phenotype of monocytic cells

Glioblastoma multiforme (GBM) is the most common primary brain tumor and is without exception lethal. GBMs modify the immune system, which contributes to the aggressive nature of the disease. Particularly, cells of the monocytic lineage, including monocytes, macrophages and microglia, are affected. We investigated the influence of GBM-derived extracellular vesicles (EVs) on the phenotype of monocytic cells. Proteomic profiling showed GBM EVs to be enriched with proteins functioning in extracellular matrix interaction and leukocyte migration. GBM EVs appeared to skew the differentiation of peripheral blood-derived monocytes to alternatively activated/M2-type macrophages. This was observed for EVs from an established cell line, as well as for EVs from primary cultures of GBM stem-like cells (GSCs). Unlike EVs of non-GBM origin, GBM EVs induced modified expression of cell surface proteins, modified cytokine secretion (e.g., an increase in vascular endothelial growth factor and IL-6) and increased phagocytic capacity of the macrophages. Most pronounced effects were observed upon incubation with EVs from mesenchymal GSCs. GSC EVs also affected primary human microglia, resulting in increased expression of Membrane type 1-matrix metalloproteinase, a marker for GBM microglia and functioning as tumor-supportive factor. In conclusion, GBM-derived EVs can modify cells of the monocytic lineage, which acquire characteristics that resemble the tumor-supportive phenotypes observed in patients.

Mesenchymal stem cells are efficiently transduced with adenoviruses bearing type 35-derived fibers and the transduced cells with the IL-28A gene produces cytotoxicity to lung carcinoma cells co-cultured

BACKGROUND

Transduction of human mesenchymal stem cells (MSCs) with type 5 adenoviruses (Ad5) is limited in the efficacy because of the poor expression level of the coxsackie adenovirus receptor (CAR) molecules. We examined a possible improvement of Ad-mediated gene transfer in MSCs by substituting the fiber region of type 5 Ad with that of type 35 Ad.

METHODS

Expression levels of CAR and CD46 molecules, which are the major receptors for type 5 and type 35 Ad, respectively, were assayed with flow cytometry. We constructed vectors expressing the green fluorescent protein gene with Ad5 or modified Ad5 bearing the type 35 fiber region (AdF35), and examined the infectivity to MSCs with flow cytometry. We investigated anti-tumor effects of MSCs transduced with interleukin (IL)-28A gene on human lung carcinoma cells with a colorimetric assay. Expression of IL-28A receptors was tested with the polymerase chain reaction. A promoter activity of transcriptional regulatory regions in MSCs was determined with a luciferase assay and a tumor growth-promoting ability of MSCs was tested with co-injection of human tumor cells in nude mice.

RESULTS

MSCs expressed CD46 but scarcely CAR molecules, and subsequently were transduced with AdF35 but not with Ad5. Growth of MSCs transduced with the IL-28A gene remained the same as that of untransduced cells since MSCs were negative for the IL-28A receptors. The IL-28A-transduced MSCs however suppressed growth of lung carcinoma cells co-cultured, whereas MSCs transduced with AdF35 expressing the β-galactosidase gene did not. A regulatory region of the cyclooygenase-2 gene possessed transcriptional activities greater than other tumor promoters but less than the cytomegalovirus promoter, and MSCs themselves did not support tumor growth in vivo.

CONCLUSIONS

AdF35 is a suitable vector to transduce MSCs that are resistant to Ad5-mediated gene transfer. MSCs infected with AdF35 that activate an exogenous gene by the cytomegalovirus promoter can be a vehicle to deliver the gene product to targeted cells.

Adenoviral vector delivery of RNA-guided CRISPR/Cas9 nuclease complexes induces targeted mutagenesis in a diverse array of human cells

CRISPR/Cas9-derived RNA-guided nucleases (RGNs) are DNA targeting systems, which are rapidly being harnessed for gene regulation and gene editing purposes in model organisms and cell lines. As bona fide gene delivery vehicles, viral vectors may be particularly fit to broaden the applicability of RGNs to other cell types including dividing and quiescent primary cells. Here, the suitability of adenoviral vectors (AdVs) for delivering RGN components into various cell types is investigated. We demonstrate that AdVs, namely second-generation fiber-modified AdVs encoding Cas9 or single guide RNA (gRNA) molecules addressing the Cas9 nuclease to the AAVS1 "safe harbor" locus or to a recombinant model allele can be produced to high-titers (up to 20 × 10(10) transducing units/ml). Importantly, AdV-mediated transduction of gRNA:Cas9 ribonucleoprotein complexes into transformed and non-transformed cells yields rates of targeted mutagenesis similar to or approaching those achieved by isogenic AdVs encoding TALENs targeting the same AAVS1 chromosomal region. RGN-induced gene disruption frequencies in the various cell types ranged from 18% to 65%. We conclude that AdVs constitute a valuable platform for introducing RGNs into human somatic cells regardless of their transformation status. This approach should aid investigating the potential and limitations of RGNs in numerous experimental settings.

Development of an AdEasy-based system to produce first- and second-generation adenoviral vectors with tropism for CAR- or CD46-positive cells

BACKGROUND

The AdEasy system has acquired preeminence amongst the various methods for producing first-generation, early region 1 (E1)-deleted human adenovirus (HAdV) vectors (AdVs) as a result of the fast and reproducible recovery of full-length AdV genomes via homologous recombination in Escherichia coli.

METHODS

From the classical AdEasy system, a new production platform was derived to assemble first- and second-generation [i.e. E1- plus early region 2A (E2A)-deleted] AdVs displaying on their surface HAdV serotype 5 (HAdV5) fibers (F5) or chimeric fibers (F5/50) comprising the tail of F5 and the fiber shaft and knob of HAdV serotype 50 (HAdV50). The CD46-interacting chimeric fibers allow for the high-level transduction of various human primary cell types of clinical interest with low or no surface expression of the Coxsackievirus and adenovirus receptor.

RESULTS

A new set of pAdEasy plasmid 'backbones' with or without E2A and encoding F5 or F5/50 was constructed and recombined in E. coli strain BJ5183 with a 'shuttle' plasmid coding for β-galactosidase. The resulting clones yielded AdV preparations with similar high titers following their rescue and propagation in producer cells. The AdVs with F5/50 were superior to those carrying F5 with respect to transducing human skeletal myocytes and mesenchymal stem cells.

CONCLUSIONS

In the present study, an AdEasy system tailored for the production of not only first-, but also second-generation AdVs equipped with the receptor-interacting fiber domains of the prototypic species C HAdV5 or of the species B member HAdV50 is presented. This system expands the range of applications for this robust and versatile AdV production platform.

Differential integrity of TALE nuclease genes following adenoviral and lentiviral vector gene transfer into human cells

The array of genome editing strategies based on targeted double-stranded DNA break formation have recently been enriched through the introduction of transcription activator-like type III effector (TALE) nucleases (TALENs). To advance the testing of TALE-based approaches, it will be crucial to deliver these custom-designed proteins not only into transformed cell types but also into more relevant, chromosomally stable, primary cells. Viral vectors are among the most effective gene transfer vehicles. Here, we investigated the capacity of human immunodeficiency virus type 1- and adenovirus-based vectors to package and deliver functional TALEN genes into various human cell types. To this end, we attempted to assemble particles of these two vector classes, each encoding a monomer of a TALEN pair targeted to a bipartite sequence within the AAVS1 ‘safe harbor’ locus. Vector DNA analyses revealed that adenoviral vectors transferred intact TALEN genes, whereas lentiviral vectors failed to do so, as shown by their heterogeneously sized proviruses in target cells. Importantly, adenoviral vector-mediated TALEN gene delivery resulted in site-specific double-stranded DNA break formation at the intended AAVS1 target site at similarly high levels in both transformed and non-transformed cells. In conclusion, we demonstrate that adenoviral, but not lentiviral, vectors constitute a valuable TALEN gene delivery platform.

Histone deacetylase inhibition activates transgene expression from integration-defective lentiviral vectors in dividing and non-dividing cells

Integration-defective lentiviral vectors (IDLVs) are being increasingly deployed in both basic and preclinical gene transfer settings. Often, however, the IDLV transgene expression profile is muted when compared to that of their integration-proficient counterparts. We hypothesized that the episomal nature of IDLVs turns them into preferential targets for epigenetic silencing involving chromatin-remodeling histone deacetylation. Therefore, vectors carrying an array of cis-acting elements and transcriptional unit components were assembled with the aid of packaging constructs encoding either the wild-type or the class I mutant D116N integrase moieties. The transduction levels and transgene-product yields provided by each vector class were assessed in the presence and absence of the histone deacetylase (HDAC) inhibitors sodium butyrate and trichostatin A. To investigate the role of the target cell replication status, we performed experiments in growth-arrested human mesenchymal stem cells and in post-mitotic syncytial myotubes. We found that IDLVs are acutely affected by HDACs regardless of their genetic makeup or target cell replication rate. Interestingly, the magnitude of IDLV transgene expression rescue due to HDAC inhibition varied in a vector backbone- and cell type-dependent manner. Finally, investigation of histone modifications by chromatin immunoprecipitation followed by quantitative PCR (ChIP-qPCR) revealed a paucity of euchromatin marks distributed along IDLV genomes when compared to those measured on isogenic integration-competent vector templates. These findings support the view that IDLVs constitute preferential targets for epigenetic silencing involving histone deacetylation, which contributes to dampening their full transcriptional potential. Our data provide leads on how to most optimally titrate and deploy these promising episomal gene delivery vehicles.

Adenoviral vectors stimulate glucagon transcription in human mesenchymal stem cells expressing pancreatic transcription factors

Viral gene carriers are being widely used as gene transfer systems in (trans)differentiation and reprogramming strategies. Forced expression of key regulators of pancreatic differentiation in stem cells, liver cells, pancreatic duct cells, or cells from the exocrine pancreas, can lead to the initiation of endocrine pancreatic differentiation. While several viral vector systems have been employed in such studies, the results reported with adenovirus vectors have been the most promising in vitro and in vivo. In this study, we examined whether the viral vector system itself could impact the differentiation capacity of human bone-marrow derived mesenchymal stem cells (hMSCs) toward the endocrine lineage. Lentivirus-mediated expression of Pdx-1, Ngn-3, and Maf-A alone or in combination does not lead to robust expression of any of the endocrine hormones (i.e. insulin, glucagon and somatostatin) in hMSCs. Remarkably, subsequent transduction of these genetically modified cells with an irrelevant early region 1 (E1)-deleted adenoviral vector potentiates the differentiation stimulus and promotes glucagon gene expression in hMSCs by affecting the chromatin structure. This adenovirus stimulation was observed upon infection with an E1-deleted adenovirus vector, but not after exposure to helper-dependent adenovirus vectors, pointing at the involvement of genes retained in the E1-deleted adenovirus vector in this phenomenon. Lentivirus mediated expression of the adenovirus E4-ORF3 mimics the adenovirus effect. From these data we conclude that E1-deleted adenoviral vectors are not inert gene-transfer vectors and contribute to the modulation of the cellular differentiation pathways.

Myogenic Properties of Human Mesenchymal Stem Cells Derived from Three Different Sources

Mesenchymal stem cells (MSCs) of mammals have been isolated from many tissues and are characterized by their aptitude to differentiate into bone, cartilage, and fat. Differentiation into cells of other lineages like skeletal muscle, tendon/ligament, nervous tissue, and epithelium has been attained with MSCs derived from some tissues. Whether such abilities are shared by MSCs of all tissues is unknown. We therefore compared for three human donors the myogenic properties of MSCs from adipose tissue (AT), bone marrow (BM), and synovial membrane (SM). Our data show that human MSCs derived from the three tissues differ in phenotype, proliferation capacity, and differentiation potential. The division rate of AT-derived MSCs (AT-MSCs) was distinctly higher than that of MSCs from the other two tissue sources. In addition, clear donor-specific differences in the long-term maintenance of MSC proliferation ability were observed. Although similar in their in vitro fusogenic capacity with murine myoblasts, MSCs of the three sources contributed to a different extent to skeletal muscle regeneration in vivo. Transplanting human AT-, BM-, or SM-MSCs previously transduced with a lentiviral vector encoding β-galactosidase into cardiotoxin-damaged tibialis anterior muscles (TAMs) of immunodeficient mice revealed that at 30 days after treatment the frequency of hybrid myofibers was highest in the TAMs treated with AT-MSCs. Our finding of human-specific β-spectrin and dystrophin in hybrid myofibers containing human nuclei argues for myogenic programming of MSCs in regenerating murine skeletal muscle. For the further development of MSC-based treatments of myopathies, AT-MSCs appear to be the best choice in view of their efficient contribution to myoregeneration, their high ex vivo expansion potential, and because their harvesting is less demanding than that of BM- or SM-MSCs.

Pressure ulcers: description of a new model and use of mesenchymal stem cells for repair

BACKGROUND

Pressure ulcers (PUs) still represent a heavy burden on many patients and nursing institutions. Our understanding of the pathophysiology and development of new treatments are hampered by the scarcity of suitable animal models.

OBJECTIVE

Evaluation of the translational value of an easily accessible mouse model.

METHODS

PUs were induced by application of magnetic devices on the dorsal skin of mice, which causes localized ischemia. The extent of the lesions and healing rate were quantified. Variations in ischemic exposure time were compared in hairless and normal mice. A detailed histological analysis of regeneration is presented. The influence of streptozotocin-induced diabetes, skin X-irradiation and treatment of the ulcers with human mesenchymal stem cells (MSCs) was investigated using immunodeficient NOD/SCID mice.

RESULTS

Ulcers induced by this form of ischemia have many features in common with decubitus ulcers in humans. No difference between hairy and hairless mice was observed in the rate of healing of the PUs. Unexpectedly, healing was not delayed in diabetic mice, but skin X-irradiation prior to ischemia resulted in a doubling of the time to complete closure of the PUs, and delayed repair of the dermis and panniculus carnosus muscle. Intradermal transplantation of human MSCs did not accelerate healing. The grafted MSCs were short-lived and only marginally participated in regeneration by differentiating into tissue-specific cells.

CONCLUSION

The results emphasize the difference in the characteristics of PUs as compared to surgical wounds. This experimental model is recommended for preclinical research on decubitus ulcers because of its mechanistic similarity with clinical PUs and its simplicity.

Mesenchymal stem cells as carriers and amplifiers in CRAd delivery to tumors

Background

Mesenchymal stem cells (MSCs) have been considered to be the attractive vehicles for delivering therapeutic agents toward various tumor diseases. This study was to explore the distribution pattern, kinetic delivery of adenovirus, and therapeutic efficacy of the MSC loading of E1A mutant conditionally replicative adenovirus Adv-Stat3(-) which selectively replicated and expressed high levels of anti-sense Stat3 complementary DNA in breast cancer and melanoma cells.

Methods

We assessed the release ability of conditionally replicative adenovirus (CRAd) from MSC using crystal violet staining, TCID₅₀ assay, and quantitative PCR. In vitro killing competence of MSCs carrying Adv-Stat3(-) toward breast cancer and melanoma was performed using co-culture system of transwell plates. We examined tumor tropism of MSC by Prussian blue staining and immunofluorescence. In vivo killing competence of MSCs carrying Adv-Stat3(-) toward breast tumor was analyzed by comparison of tumor volumes and survival periods.

Results

Adv-Stat3(-) amplified in MSCs and were released 4 days after infection. MSCs carrying Adv-Stat3(-) caused viral amplification, depletion of Stat3 and its downstream proteins, and led to significant apoptosis in breast cancer and melanoma cell lines. In vivo experiments confirmed the preferential localization of MSCs in the tumor periphery 24 hours after tail vein injection, and this localization was mainly detected in the tumor parenchyma after 72 hours. Intravenous injection of MSCs carrying Adv-Stat3(-) suppressed the Stat3 pathway, down-regulated Ki67 expression, and recruited CD11b-positive cells in the local tumor, inhibiting tumor growth and increasing the survival of tumor-bearing mice.

Conclusions

These results indicate that MSCs migrate to the tumor site in a time-dependent manner and could be an effective platform for the targeted delivery of CRAd and the amplification of tumor killing effects.

Exploitation of herpesvirus immune evasion strategies to modify the immunogenicity of human mesenchymal stem cell transplants

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent cells residing in the connective tissue of many organs and holding great potential for tissue repair. In culture, human MSCs (hMSCs) are capable of extensive proliferation without showing chromosomal aberrations. Large numbers of hMSCs can thus be acquired from small samples of easily obtainable tissues like fat and bone marrow. MSCs can contribute to regeneration indirectly by secretion of cytokines or directly by differentiation into specialized cell types. The latter mechanism requires their long-term acceptance by the recipient. Although MSCs do not elicit immune responses in vitro, animal studies have revealed that allogeneic and xenogeneic MSCs are rejected.

METHODOLOGY/PRINCIPAL FINDINGS

We aim to overcome MSC immune rejection through permanent down-regulation of major histocompatibility complex (MHC) class I proteins on the surface of these MHC class II-negative cells through the use of viral immune evasion proteins. Transduction of hMSCs with a retroviral vector encoding the human cytomegalovirus US11 protein resulted in strong inhibition of MHC class I surface expression. When transplanted into immunocompetent mice, persistence of the US11-expressing and HLA-ABC-negative hMSCs at levels resembling those found in immunodeficient (i.e., NOD/SCID) mice could be attained provided that recipients' natural killer (NK) cells were depleted prior to cell transplantation.

CONCLUSIONS/SIGNIFICANCE

Our findings demonstrate the potential utility of herpesviral immunoevasins to prevent rejection of xenogeneic MSCs. The observation that down-regulation of MHC class I surface expression renders hMSCs vulnerable to NK cell recognition and cytolysis implies that multiple viral immune evasion proteins are likely required to make hMSCs non-immunogenic and thereby universally transplantable.

Long-term contribution of human bone marrow mesenchymal stromal cells to skeletal muscle regeneration in mice

Mesenchymal stromal cells (MSCs) are attractive for cellular therapy of muscular dystrophies as they are easy to procure, can be greatly expanded ex vivo, and contribute to skeletal muscle repair in vivo. However, detailed information about the contribution of bone marrow (BM)-derived human MSCs (BM-hMSCs) to skeletal muscle regeneration in vivo is very limited. Here, we present the results of a comprehensive study of the fate of LacZ-tagged BM-hMSCs following implantation in cardiotoxin (CTX)-injured tibialis anterior muscles (TAMs) of immunodeficient mice. β-Galactosidase-positive (β-gal(+)) human-mouse hybrid myofibers (HMs) were counted in serial cross sections over the full length of the treated TAMs of groups of mice at monthly intervals. The number of human cells was estimated using chemiluminescence assays. While the number of human cells declined gradually to about 10% of the injected cells at 60 days after transplantation, the number of HMs increased from day 10 onwards, reaching 104 ± 39.1 per TAM at 4 months postinjection. β-gal(+) cells and HMs were distributed over the entire muscle, indicating migration of the former from the central injection site to the ends of the TAMs. The identification of HMs that stained positive for human spectrin suggests myogenic reprogramming of hMSC nuclei. In summary, our findings reveal that BM-hMSCs continue to participate in the regeneration/remodeling of CTX-injured TAMs, resulting in ±5% HMs at 4 months after damage induction. Moreover, donor-derived cells were shown to express genetic information, both endogenous and transgenic, in recipient myofibers.

Molecular image analysis: quantitative description and classification of the nuclear lamina in human mesenchymal stem cells

The nuclear lamina is an intermediate filament network that provides a structural framework for the cell nucleus. Changes in lamina structure are found during changes in cell fate such as cell division or cell death and are associated with human diseases. An unbiased method that quantifies changes in lamina shape can provide information on cells undergoing changes in cellular functions. We have developed an image processing methodology that finds and quantifies the 3D structure of the nuclear lamina. We show that measurements on such images can be used for cell classification and provide information concerning protein spatial localization in this structure. To demonstrate the efficacy of this method, we compared the lamina of unmanipulated human mesenchymal stem cells (hMSCs) at passage 4 to cells activated for apoptosis. A statistically significant classification was found between the two populations.

Branched oligomerization of cell-permeable peptides markedly enhances the transduction efficiency of adenovirus into mesenchymal stem cells

Cell-permeable peptides (CPPs) promote the transduction of nonpermissive cells by recombinant adenovirus (rAd) to improve the therapeutic efficacy of rAd. In this study, branched oligomerization of CPPs significantly enhanced the transduction of human mesenchymal stem cells (MSCs) by rAd in a CPP type-independent manner. In particular, tetrameric CPPs increased transduction efficiency at 3000-5000-fold lower concentrations than did monomeric CPPs. Although branched oligomerization of CPPs also increases cytotoxicity, optimal concentrations of tetrameric CPPs required for maximum transduction are at least 300-1000-fold lower than those causing 50% cytotoxicity. Furthermore, although only approximately 60% of MSCs were maximally transduced at 500 muM of monomeric CPPs, >95% of MSCs were transduced with 0.1 muM of tetrameric CPPs. Tetrameric CPPs also significantly increased the formation and net surface charge of CPP/rAd complexes, as well as the binding of rAd to cell membranes at a greater degree than did monomeric CPPs, followed by rapid internalization into MSCs. In a critical-size calvarial defect model, the inclusion of tetrameric CPPs in ex vivo transduction of rAd expressing bone morphogenetic protein 2 into MSCs promoted highly mineralized bone formation. In addition, MSCs that were transduced with rAd expressing brain-derived neurotrophic factor in the presence of tetrameric CPPs improved functional recovery in a spinal cord injury model. These results demonstrated the potential for tetrameric CPPs to provide an innovative tool for MSC-based gene therapy and for in vitro gene delivery to MSCs.

Fiber-modified adenovirus can mediate human adipose tissue-derived mesenchymal stem cell-based anti-angiogenic gene therapy

A fiber-modified adenovirus (rAd5F11B), loaded with the Kringle1-5 gene (rAd-K1-5) was used to infect human adipose tissue-derived mesenchymal stem cells (HAMSCs). At a multiplicity of infection of 20, the transfection efficiency in HAMSCs was 90% and the cell expansion and differentiation of infected HAMSCs were not significantly suppressed. HAMSCs infected with rAd-K1-5 expressed the exogenous Kringle1-5 protein, an angiogenic inhibitor, and conditioned media from HAMSCs expressing the Kringle1-5 protein blocked VEGF-induced neovascularization both in vitro and in vivo. rAd5F11B may therefore be a promising gene transfer vector in HAMSCs-based anti-angiogenic gene therapy because of its low toxicity and high transfection efficiency.

Directing systemic oncolytic viral delivery to tumors via carrier cells

The systemic administration of oncolytic virus (OV) is often inefficient due to clearance of the virus by host defense mechanism and spurious targeting of non-cancer tissues through the bloodstream. Cell mediated OV delivery could hide the virus from host defenses and direct them toward tumors: Mesenchymal and neural stem cells have been described to possess tumor-homing ability as well as the capacity to deliver OVs. In this review, we will focus on approaches where OV and carrier cells are utilized for cancer therapy. Effective cellular internalization and replication of OVs need to occur both in cancer and carrier cells. We thus will discuss the current challenges faced by the use of OV delivery via carrier cells.

The nuclear lamina promotes telomere aggregation and centromere peripheral localization during senescence of human mesenchymal stem cells

Ex vivo, human mesenchymal stem cells (hMSCs) undergo spontaneous cellular senescence after a limited number of cell divisions. Intranuclear structures of the nuclear lamina were formed in senescent hMSCs, which are identified by the presence of Hayflick-senescence-associated factors. Notably, spatial changes in lamina shape were observed before the Hayflick senescence-associated factors, suggesting that the lamina morphology can be used as an early marker to identify senescent cells. Here, we applied quantitative image-processing tools to study the changes in nuclear architecture during cell senescence. We found that centromeres and telomeres colocalised with lamina intranuclear structures, which resulted in a preferred peripheral distribution in senescent cells. In addition, telomere aggregates were progressively formed during cell senescence. Once formed, telomere aggregates showed colocalization with gamma-H2AX but not with TERT, suggesting that telomere aggregates are sites of DNA damage. We also show that telomere aggregation is associated with lamina intranuclear structures, and increased telomere binding to lamina proteins is found in cells expressing lamina mutants that lead to increases in lamina intranuclear structures. Moreover, three-dimensional image processing revealed spatial overlap between telomere aggregates and lamina intranuclear structures. Altogether, our data suggest a mechanical link between changes in lamina spatial organization and the formation of telomere aggregates during senescence of hMSCs, which can possibly contribute to changes in nuclear activity during cell senescence.

Gene therapy using TRAIL-secreting human umbilical cord blood-derived mesenchymal stem cells against intracranial glioma

Adenovirus-mediated gene therapies against brain tumors have been limited by the difficulty in tracking glioma cells infiltrating the brain parenchyma. Human umbilical cord blood-derived mesenchymal stem cells (UCB-MSC) are particularly attractive cells for clinical use in cell-based therapies. In the present study, we evaluated the tumor targeting properties and antitumor effects of UCB-MSCs as gene delivery vehicles for glioma therapy. We efficiently engineered UCB-MSCs to deliver a secretable trimeric form of tumor necrosis factor-related apoptosis-inducing ligand (stTRAIL) via adenoviral transduction mediated by cell-permeable peptides. We then confirmed the migratory capacity of engineered UCB-MSCs toward tumor cells by an in vitro migration assay and by in vivo injection of UCB-MSCs into the tumor mass or the opposite hemisphere of established human glioma in nude mice. Moreover, in vitro coculture, experiments on Transwell plates, and in vivo survival experiments showed that MSC-based stTRAIL gene delivery has more therapeutic efficacy compared with direct injection of adenovirus encoding the stTRAIL gene into a tumor mass. In vivo efficacy experiments showed that intratumoral injection of engineered UCB-MSCs (MSCs-stTRAIL) significantly inhibited tumor growth and prolonged the survival of glioma-bearing mice compared with controls. These results suggest that human UCB-MSCs have potential use as effective delivery vehicles for therapeutic genes in the treatment of intracranial glioma.

Targeted chromosomal insertion of large DNA into the human genome by a fiber-modified high-capacity adenovirus-based vector system

A prominent goal in gene therapy research concerns the development of gene transfer vehicles that can integrate exogenous DNA at specific chromosomal loci to prevent insertional oncogenesis and provide for long-term transgene expression. Adenovirus (Ad) vectors arguably represent the most efficient delivery systems of episomal DNA into eukaryotic cell nuclei. The most advanced recombinant Ads lack all adenoviral genes. This renders these so-called high-capacity (hc) Ad vectors less cytotoxic/immunogenic than those only deleted in early regions and creates space for the insertion of large/multiple transgenes. The versatility of hcAd vectors is been increased by capsid modifications to alter their tropism and by the incorporation into their genomes of sequences promoting chromosomal insertion of exogenous DNA. Adeno-associated virus (AAV) can insert its genome into a specific human locus designated AAVS1. Trans- and cis-acting elements needed for this reaction are the AAV Rep78/68 proteins and Rep78/68-binding sequences, respectively. Here, we describe the generation, characterization and testing of fiber-modified dual hcAd/AAV hybrid vectors (dHVs) containing both these elements. Due to the inhibitory effects of Rep78/68 on Ad-dependent DNA replication, we deployed a recombinase-inducible gene switch to repress Rep68 synthesis during vector rescue and propagation. Flow cytometric analyses revealed that rep68-positive dHVs can be produced similarly well as rep68-negative control vectors. Western blot experiments and immunofluorescence microscopy analyses demonstrated transfer of recombinase-dependent rep68 genes into target cells. Studies in HeLa cells and in the dystrophin-deficient myoblasts from a Duchenne muscular dystrophy (DMD) patient showed that induction of Rep68 synthesis in cells transduced with fiber-modified and rep68-positive dHVs leads to increased stable transduction levels and AAVS1-targeted integration of vector DNA. These results warrant further investigation especially considering the paucity of vector systems allowing permanent phenotypic correction of patient-own cell types with large DNA (e.g. recombinant full-length DMD genes).

Genetic complementation of human muscle cells via directed stem cell fusion

Duchenne muscular dystrophy (DMD) is caused by mutations in the X chromosome-linked DMD gene, which encodes the sarcolemma-stabilizing protein-dystrophin. Initial attempts at DMD therapy deployed muscle progenitor cells from healthy donors. The utilization of these cells is, however, hampered by their immunogenicity, while those from DMD patients are scarce and display limited ex vivo replication. Nonmuscle cells with myogenic capacity may offer valuable alternatives especially if, to allow autologous transplantation, they are amenable to genetic intervention. As a paradigm for therapeutic gene transfer by heterotypic cell fusion we are investigating whether human mesenchymal stem cells (hMSCs) can serve as donors of recombinant DMD genes for recipient human muscle cells. Here, we show that forced MyoD expression in hMSCs greatly increases their tendency to participate in human myotube formation turning them into improved DNA delivery vehicles. Efficient loading of hMSCs with recombinant DMD was achieved through a new tropism-modified high-capacity adenoviral (hcAd) vector directing striated muscle-specific synthesis of full-length dystrophin. This study introduces the principle of genetic complementation of gene-defective cells via directed cell fusion and provides an initial framework to test whether transient MyoD synthesis in autologous, gene-corrected hMSCs increases their potential for treating DMD and, possibly, other muscular dystrophies.

Mesenchymal stem cells effectively deliver an oncolytic adenovirus to intracranial glioma

Gene therapy represents a promising treatment alternative for patients with malignant gliomas. Nevertheless, in the setting of these highly infiltrative tumors, transgene delivery remains a challenge. Indeed, viral vehicles tested in clinical trials often target only those tumor cells that are adjacent to the injection site. In this study, we examined the feasibility of using human mesenchymal stem cells (hMSC) to deliver a replication-competent oncolytic adenovirus (CRAd) in a model of intracranial malignant glioma. To do so, CRAds with a chimeric 5/3 fiber or RGD backbone with or without CXCR4 promoter driving E1A were examined with respect to replication and toxicity in hMSC, human astrocytes, and the human glioma cell line U87MG by quantitative polymerase chain reaction and membrane integrity assay. CRAd delivery by virus-loaded hMSC was then evaluated in vitro and in an in vivo model of mice bearing intracranial U87MG xenografts. Our results show that hMSC are effectively infected by CRAds that use the CXCR4 promoter. CRAd-CXCR4-RGD had the highest replication, followed by CRAd-CXCR4-5/3, in hMSC, with comparable levels of toxicity. In U87MG tumor cells, CRAd-CXCR4-5/3 showed the highest replication and toxicity. Virus-loaded hMSC effectively migrated in vitro and released CRAds that infected U87MG glioma cells. When injected away from the tumor site in vivo, hMSC migrated to the tumor and delivered 46-fold more viral copies than injection of CRAd-CXCR4-5/3 alone. Taken together, these results indicate that hMSC migrate and deliver CRAd to distant glioma cells. This delivery strategy should be explored further, as it could improve the outcome of oncolytic virotherapy for glioma.

Human mesenchymal stem cells lack tumor tropism but enhance the antitumor activity of oncolytic adenoviruses in orthotopic lung and breast tumors

Systemic adenoviral delivery into tumors is inefficient because of liver sequestration of intravenously administered virus. One potential solution for improving bioavailability is the use of carrier cells such as human mesenchymal stem cells (MSCs), which have been suggested to have inherent tumor tropism. Here we investigated the capacity of capsid-modified adenoviruses to infect and replicate in MSCs. Further, biodistribution and tumor-killing efficacy of MSCs loaded with oncolytic adenoviruses were evaluated in orthotopic murine models of lung and breast cancer. In vitro, heparan sulfate proteoglycan- and alpha(v)beta integrin-targeted viruses enhanced gene delivery to bone marrow- and adipose tissue-derived MSCs up to 11,000-fold over adenovirus serotype 5 (Ad5). Infectivity-enhanced oncolytic adenoviruses showed notably higher rates of cytolysis of in vitro-passaged MSCs in comparison with wild-type virus. In vivo, intravenously injected MSCs homed primarily to the lungs, and virus was released into advanced orthotopic breast and lung tumors for therapeutic efficacy and increased survival. When the same dose of virus was injected intravenously without MSCs, only transduction of the liver was seen. These results suggest that MSCs loaded with oncolytic adenoviruses might be a useful approach for improving the bioavailability of systemically administered oncolytic adenoviruses.

An effective method for adenoviral-mediated delivery of small interfering RNA into mesenchymal stem cells

Mesenchymal stem cells (MSCs) promise as a main actor of cell-based therapeutic strategies, due to their intrinsic ability to differentiate along different mesenchymal cell lineages, able to repair the diseased or injured tissue in which they are localized. The application of MSCs in therapies requires an in depth knowledge of their biology and of the molecular mechanisms leading to MSC multilineage differentiation. The knockdown of target genes through small interfering RNA (siRNA) carried by adenoviruses (Ad) represents a valid tool for the study of the role of specific molecules in cell biology. Unfortunately, MSCs are poorly transfected by conventional Ad serotype 5 (Ad5) vectors. We set up a method to obtain a very efficient transduction of rat MSCs with low doses of unmodified Ad5, carrying the siRNA targeted against the mRNA coding for Rb2/p130 (Ad-siRNA-Rb2), which plays a fundamental role in cell differentiation. This method allowed a 95% transduction rate of Ad-siRNA in MSC, along with a siRNA-mediated 85% decrease of Rb2/p130 mRNA and a 70% decrease of Rb2/p130 protein 48 h after transduction with 50 multiplicities of infection (MOIs) of Ad5. The effect on Rb2/p130 protein persisted 15 days after transduction. Finally, Ad-siRNA did not compromise the viability of transduced MSCs neither induced any cell cycle modification. The effective Ad-siRNA-Rb2 we constructed, together with the efficient method of delivery in MSCs we set up, will allow an in depth analysis of the role of Rb2/p130 in MSC biology and multilineage differentiation.

Changes in lamina structure are followed by spatial reorganization of heterochromatic regions in caspase-8-activated human mesenchymal stem cells

Apoptosis is fundamental to the regulation of homeostasis of stem cells in vivo. Whereas the pathways underlying the molecular and biochemical details of nuclear breakdown that accompanies apoptosis have been elucidated, the precise nature of nuclear reorganization that precedes the demolition phase is not fully understood. Here, we expressed an inducible caspase-8 in human mesenchymal stem cells, and quantitatively followed the early changes in nuclear organization during apoptosis. We found that caspase-8 induces alteration of the nuclear lamina and a subsequent spatial reorganization of both centromeres, which are shifted towards a peripheral localization, and telomeres, which form aggregates. This nuclear reorganization correlates with caspase-3 sensitivity of lamina proteins, because the expression of lamin mutant constructs with caspase-3 hypersensitivity resulted in a caspase-8-independent appearance of lamina intranuclear structures and telomere aggregates, whereas application of a caspase inhibitor restrains these changes in nuclear reorganization. Notably, upon activation of apoptosis, we observed no initial changes in the spatial organization of the promyelocytic leukemia nuclear bodies (PML-NBs). We suggest that during activation of the caspase-8 pathway changes in the lamina structure precede changes in heterochromatin spatial organization, and the subsequent breakdown of lamina and PML-NB.

A new group B adenovirus receptor is expressed at high levels on human stem and tumor cells

CD46 is used by human group B adenoviruses (Ads) as a high-affinity attachment receptor. Here we show evidence that several group B Ads utilize an additional receptor for infection of human cells, which is different from CD46. We tentatively named this receptor receptor X. Competition studies with unlabeled and labeled Ads, recombinant Ad fiber knobs, and soluble CD46 and CD46 antibodies revealed three different subgroups of group B Ads, in terms of their receptor usage. Group I (Ad16, -21, -35, and -50) nearly exclusively uses CD46. Group II (Ad3, -7p, and -14) utilizes receptor X and not CD46. Group III (Ad11p) uses both CD46 and the alternative receptor X. Interaction of group II and III Ads with receptor X occurs via the fiber knob. Receptor X is an abundantly expressed glycoprotein that interacts with group II and III Ads at relatively low affinity in a Ca(2+)-dependent manner. This receptor is expressed at high levels on human mesenchymal and undifferentiated embryonic stem cells, as well as on human cancer cell lines. These findings have practical implications for stem cell and gene therapy.

Epicardial cells of human adults can undergo an epithelial-to-mesenchymal transition and obtain characteristics of smooth muscle cells in vitro

Myocardial and coronary development are both critically dependent on epicardial cells. During cardiomorphogenesis, a subset of epicardial cells undergoes an epithelial-to-mesenchymal transition (EMT) and invades the myocardium to differentiate into various cell types, including coronary smooth muscle cells and perivascular and cardiac interstitial fibroblasts. Our current knowledge of epicardial EMT and the ensuing epicardium-derived cells (EPDCs) comes primarily from studies of chick and mouse embryonic development. Due to the absence of an in vitro culture system, very little is known about human EPDCs. Here, we report for the first time the establishment of cultures of primary epicardial cells from human adults and describe their immunophenotype, transcriptome, transducibility, and differentiation potential in vitro. Changes in morphology and beta-catenin staining pattern indicated that human epicardial cells spontaneously undergo EMT early during ex vivo culture. The surface antigen profile of the cells after EMT closely resembles that of subepithelial fibroblasts; however, only EPDCs express the cardiac marker genes GATA4 and cardiac troponin T. After infection with an adenovirus vector encoding the transcription factor myocardin or after treatment with transforming growth factor-beta1 or bone morphogenetic protein-2, EPDCs obtain characteristics of smooth muscle cells. Moreover, EPDCs can undergo osteogenesis but fail to form adipocytes or endothelial cells in vitro. Cultured epicardial cells from human adults recapitulate at least part of the differentiation potential of their embryonic counterparts and represent an excellent model system to explore the biological properties and therapeutic potential of these cells.

Adenovirus vector-mediated gene transfer into stem cells

Stem cells, including embryonic stem (ES) cells, mesenchymal stem cells (MSCs), and hematopoietic stem cells (HSCs), are defined by their capacity for self-renewal and multilineage differentiation. Efficient gene transfer into stem cells is essential for the basic research in developmental biology and for therapeutic applications in gene-modified regenerative medicine. Adenovirus (Ad) vectors, based on Ad type 5, can efficiently and transiently introduce the exogenous gene into many cell types via the primary receptor, coxsackievirus, and adenovirus receptor (CAR). However, some kinds of stem cells, such as MSCs and HSCs, cannot be efficiently transduced with conventional Ad vectors based on Ad serotype 5 (Ad5), because of the lack of CAR expression. To overcome this problem, fiber-modified Ad vectors and an Ad vector based on another serotype of Ad have been developed. Here, we review the advances in the development of Ad vectors suitable for stem cells and discuss their application in basic biology and clinical medicine.

Human mesenchymal stem cells ectopically expressing full-length dystrophin can complement Duchenne muscular dystrophy myotubes by cell fusion

Duchenne muscular dystrophy (DMD) is the most prevalent inheritable muscle disease. It is caused by mutations in the approximately 2.5-megabase dystrophin (Dys) encoding gene. Therapeutic attempts at DMD have relied on injection of allogeneic Dys-positive myoblasts. The immune rejection of these cells and their limited availability have prompted the search for alternative therapies and sources of myogenic cells. Stem cell-based gene therapy aims to restore tissue function by the transplantation of gene-corrected autologous cells. It depends on (i) the capacity of stem cells to participate in tissue regeneration and (ii) the efficient genetic correction of defective autologous stem cells. We explored the potential of bone marrow-derived human mesenchymal stem cells (hMSCs) genetically modified with the full-length Dys-coding sequence to engage in myogenesis. By tagging hMSCs with enhanced green fluorescent protein (EGFP) or the membrane dye PKH26, we demonstrated that they could participate in myotube formation when cultured together with differentiating human myoblasts. Experiments performed with EGFP-marked hMSCs and DsRed-labeled DMD myoblasts revealed that the EGFP-positive DMD myotubes were also DsRed-positive indicating that hMSCs participate in human myogenesis through cellular fusion. Finally, we showed that hMSCs transduced with a tropism-modified high-capacity hybrid viral vector encoding full-length Dys could complement the genetic defect of DMD myotubes.